Problem: Kong took $15\%$ fewer seconds than Nolan took to complete his multiplication timed test. Kong took $85$ seconds. How many seconds did Nolan take?
Answer: Kong took $15\%$ fewer seconds than Nolan took. So Kong took $100\%-15\%=85\%$ as many seconds as Nolan took. Percent means per hundred, so ${85\%}$ is equivalent to ${\dfrac{85}{100}}$ which is also equal to ${85\div 100}$. ${85\div 100 = 0.85}$ Kong took ${85}$ seconds $(\text{s})$. To find the number of seconds Nolan took, we need to answer, ${85\,\text{s}}$ is ${85\%}$ of what length of time? We can rewrite that question as an equation. $\begin{array}{ccccc} {85\,\text{s}}&\text{is}&{85\%}&\text{of}&\text{what length of time}\\\\ {85}&=&{0.85}&\times&? \end{array}$ Let's solve for the unknown length of time. $\begin{aligned} \dfrac{{85}}{0.85}&=\dfrac{{0.85}\times?}{0.85}\\\\ 100&=? \end{aligned}$ Nolan took $100$ seconds.